The Internal Revenue Service encourages taxpayers who typically itemized their deductions on Schedule A of the Form 1040 to use the Withholding Calculator this year to perform a “paycheck checkup.”

People who have itemized before may be affected by changes from the Tax Cuts and Jobs Act. Taxpayers who itemize should use the IRS Withholding Calculator to make sure their employers are withholding the appropriate amount of tax from their paychecks for their financial situation.

The law changes are effective in 2018 and affect the tax returns taxpayers will file in 2019. The new law makes a number of major changes, including:

Limiting the deductions for state and local taxes

Limiting the deduction for home mortgage interest in certain cases (see IR-2018-32 for more information)

The Tax Cuts and Jobs Act nearly doubled standard deductions and changed several itemized deductions. Some individuals who formerly itemized may now find it more beneficial to take the standard deduction, and this could affect how much a taxpayer needs to have their employer withhold from their pay. Also, even those who continue to itemize deductions should check their withholding because of changes made by the new tax law.

The IRS urges taxpayers to complete their “paycheck checkup” as early as possible so that if a withholding amount adjustment is necessary, there’s more time for withholding to take place evenly throughout the year. Waiting means there are fewer pay periods to make the tax changes – which could have a bigger impact on each paycheck.

Having too little tax withheld could result in an unexpected tax bill or penalty at tax time in 2019. Adjusting withholding after a “paycheck checkup” can also prevent employees from having too much tax withheld. With the average refund topping $2,800, some taxpayers might prefer to have less tax withheld up front and receive more in their paychecks.